A supercharged or turbocharged engine includes a compressor for increasing an amount of air flowing through the engine. The engine's output power may increase when the amount of air flowing through the engine is increased. In particular, the engine's fuel flow amount may be proportionately increased with the engine's air flow amount to increase engine power. The turbocharger's compressor increases air pressure in the engine's intake system so that air flow through the engine may be increased. However, if driver demand torque decreases, it may not be desirable to operate the engine with a higher pressure in the engine intake system because the higher air pressure may make it more difficult to control engine air flow at lower engine air flow levels. One way to quickly reduce engine intake system air pressure is to install a compressor recirculation valve in parallel with the compressor. By opening the compressor recirculation valve, pressure upstream of the compressor may be reduced so that it may be easier to operate the engine with a low engine airflow amount. Nevertheless, deposits may form in the compressor recirculation valve to make it more difficult to control engine intake pressure in a desired way.
The inventors herein have recognized the above-mentioned issues and have developed a diagnostic method, comprising: partially opening a waste gate and adjusting a compressor recirculation valve to a closed position in response to a diagnostic request; incrementally opening the compressor recirculation valve after the compressor recirculation valve is closed; adjusting a compressor recirculation valve airflow offset in response to a control parameter while incrementally opening the compressor recirculation valve from the closed position; and operating the compressor recirculation valve in response to the airflow offset.
By adjusting a compressor recirculation valve airflow offset in response to a control parameter, it may be possible to provide the technical result of improving engine air intake pressure control even when deposits are formed within a compressor recirculation valve. In one example, the recirculation valve airflow offset may be determined based on a change in position of a throttle used to maintain engine air flow. In particular, the recirculation valve may be first closed and then incrementally opened. The recirculation valve opening position where the engine throttle position is changed to maintain constant engine airflow may be determined to be the compressor recirculation valve offset value. The engine throttle position may be adjusted in response to pressure at the inlet of the throttle to maintain engine airflow and reduce the possibility of disturbing a driver.
The present description may provide several advantages. For example, the approach may improve engine airflow at low driver demand levels. Further, the approach may improve engine air-fuel ratio control during accelerator pedal tip-out conditions. Further, the approach may be applied to turbocharged or supercharged engines.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.